When someone says something to quickly or something hard to understand, I use a line by the old guy who got shot in the wooden leg by Smithers (don’t know if he has a name): “Who shot who in the what now?”
I’ve always been partial to some of the lines from the ep in which Homer wants to be more like Thomas Edison.
I can’t tell you how many work meetings, in which someone wants to implement a new process or procedure, have had to sit through the line, “Do us all a favor and invent yourself some underpants.”
That line still cracks me up.
Oh, and a second for the “I find your ideas intriguing, and I’d like to subscribe to your newsletter” gag. 
One time I answered the door wearing only my boxers because I was expecting my girlfriend at that time to be at the door. Instead it was the UPS guy. I said, matter-of-factly: “I’ve misplaced my pants.”
Also, when my wife asks me a question to which she won’t like the answer, I say: “Baby, I’m not going to lie to you. Well, gotta go.”
I too use “shot who in the whatnow?” all the time.
One of my favorites is from the episode where Lisa performs a science experiment comparing Bart’s intelligence to her hamster’s. In one phase, she wires a cupcake up to deliver a shock. Bart keeps grabbing the cupcake, despite getting shocked several times.As a result, I have come to use “BZZT! Ow! BZZT! Ow!” in situations where someone repeatedly does something stupid or painful, when they should have learned their lesson the first time.
“Hey, that didn’t work the way the man on the television said it would.”
Whenever I say “I didn’t do it,” I add, “I’m the I Didn’t Do It Girl!”
No one EVER gets the reference.
Every time I’m in some sort of 7-11 type store, I must say “Moon Pie! What a time to be alive.”
I will routinely get a footlong sub, eat half, then break out the other half in the wee hours of the morning and say (to myself) “I could never stay mad at you, sandwich.”
When I’m out with friends and everyone is suggesting restaurant names, I will inevitably say “Professor P.J. Cornucopia’s Fantastic Foodmagorium and Great American Steakery?”
Friends / relatives frequently ask me to help them with their computer problems, offering to pay me. This leads to this exchange:
“Don’t worry about that - I’ll do it Pro Boner.”
“Don’t you mean pro-bono?”
“I know what I said.”
I use “I am so smart! I am so smart! S-M-R-T! I mean S-M-A-R-T!” for my own crackheaded mistakes, or other folks’.
I’m pretty sure the old man is called Jasper. But someone may correct me. Not seen him in a while.
I use “NEIN!!!” a lot for no. It’s from when Mr. Burns and Marge’s mother are getting married. There’s one German in the first row and Barny yells “Down in front!!”, that’s when the German says “NEIN!!!”
“D’oh” gets used so much, I don’t even think of it as a Simpsons thing anymore. Another vote for “who shot who in the what now?”, as well.
Generally, when I go to Burger King, I order a Partially Gelatinated Gum-Based Beverage. One of these days someone’ll get it.
Others used fairly often:
“The sun is out, birds are singing, bees are trying to have sex with them…as is my understanding.”
“It’s craptacular”.
“I’m going home now…to…sleep.”
“Heh heh heh…I get it. I get jokes.”
“Idiotic, crappy <insert appropriate object/ideal here> for jerks.”
“It’s because they’re stupid, that’s why. That’s why everybody does everything.”
“That’s unpossible.”
" ‘Ray J’ funny or 'O.J. funny?"
i’m *forever * WooHooing.
also, Mmmmm… (Insert noun here)…
Anytime something surprising or extraordinary happens, I can be heard to exclaim “Sweet Merciful Crap!”. It also used to play whenever I had a new email message.
“Ladies! There’s enough Millhouse to go around!”
We recently underwent a contract transition at work - one of several times in my life that the quote “I, for one, welcome our new insect overlords…” has come in handy.
And, in the non sequitur department, I often let go with “Gah, boy … that monkey is going to pay.” in my best Professor Frink voice.
A few years ago, I was vacationing in Acapulco and on one of those touristy bus trips.
One of the stops was a hotel proudly displaying pictures of ‘famous’ movie stars that had stayed there.
This was from oh, 30 or 40 years ago, when Acapulco was the in place to be. (John Wayne staying there was a big deal.)
Everyone was pretty bored, especially the kids, because nobody really cared about these old stars. At one point my daughter, who was about 8 then, saw a picture of Rory Calhoun and got all excited. “Look Dad! Rory Calhoun!’
The tour guide just beamed. ‘You know who Rory Calhoun is?’ “Oh YES “, says my daughter happily. I didn’t have the heart to tell the guy she thought he was a Simpson’s character. (Mr. Burns: “Look at them standing there on their hind legs, like a couple of Rory Calhouns”)
“Don’t blame me, I voted for Kotos” is one of my personal faves.
I use S-M-R-T quite often too.
Another one that seems to pop up is from the episode where Homer finds an overturned sugar truck, and all the bees are on his sugar pile. “Bees are on the what now?” - used when I have no idea what the other person is talking about - found I used it a lot with my last girlfriend who would start conversations half way through having played out the first half in her head.
Another one my friends and I use is “I’LL LEARN YOU!!” followed by a very calm “What does that mean? Is that even a threat?” response.
Sounds like you may need one of these:
LionelHutz, was Rory Calhoun standing and walking in the picture? Are you sure it wasn’t Bob Barker or David Brenner?
Depending on the way things go in November, I just may get one of those bumper stickers!
I also this one whenever someone is rambling about dreams:
“Smithers, you know that dream where I fly in the window naked?”
“Mmmm…yes,sir.”
